Organometallic ruthenium complexes and related methods for the preparation of tetra-substituted and other hindered olefins

ABSTRACT

The invention relates to ruthenium alkylidene complexes having an N-heterocyclic carbene ligand comprising a 5-membered heterocyclic ring having a carbenic carbon atom and at least one nitrogen atom contained within the 5-membered heterocyclic ring, wherein the nitrogen atom is directly attached to the carbenic carbon atom and is substituted by a phenyl ring, and wherein the phenyl ring has a hydrogen at either or both ortho positions and is substituted at at least one ortho or meta position. The invention also relates to an olefin metathesis reactions and particularly to the preparation of tetra-substituted cyclic olefins via a ring-closing metathesis.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Application 60/751,225, filed Dec. 16, 2005; U.S. Application 60/801,742, filed May 19, 2006; U.S. Application 60/859,148, filed Nov. 15, 2006; and U.S. Application 60/853,717, Oct. 19, 2006; the disclosures of which are incorporated herein by reference.

The U.S. Government has certain rights in this invention pursuant to Grant No. GM031332 awarded by the National Institutes of Health.

TECHNICAL FIELD

This invention relates generally to olefin metathesis. More particularly, the invention relates to organometallic ruthenium complexes and olefin metathesis methods using them to produce hindered olefins. The catalysts and methods of the invention have utility in the fields of catalysis, organic synthesis, and industrial chemistry.

BACKGROUND OF THE INVENTION

Olefin metathesis catalysis is a powerful technology, which in recent years has received tremendous attention as a versatile method for the formation of carbon-carbon bonds and has numerous applications in organic synthesis and polymer chemistry. R. H. Grubbs, Handbook of Metathesis, Vol. 2 and 3; Wiley VCH, Weinheim, 2003. The family of olefin metathesis reactions includes, but is not limited to, ring-closing metathesis (RCM), cross metathesis (CM), ring-opening metathesis polymerization (ROMP), and acyclic diene metathesis polymerization (ADMET). The success of olefin metathesis stems from the development of several well-defined transition metal complexes, such as the Schrock molybdenum catalysts and the Grubbs ruthenium catalysts. R. H. Grubbs, Handbook of Metathesis, Vol. 1; Wiley VCH, Weinheim, 2003. The molybdenum catalysts are generally highly active but are also highly sensitive to air, moisture, and to certain functional groups present in the olefinic substrate, the reaction solvent, or impurities. The ruthenium catalysts are much more robust than the molybdenum catalysts.

The original first-generation ruthenium catalysts were primarily bisphosphine complexes of the general formula (PR₃)₂(X)₂Ru═CHR^(a) wherein X represents a halogen (e.g., Cl, Br, or I), R represents an alkyl, cycloalkyl, or aryl group (e.g., butyl, cyclohexyl, or phenyl), and R^(a) represents an alkyl, alkenyl, or aryl group (e.g., methyl, CH═CMe₂, phenyl, etc.). Examples of these types of catalysts are described in U.S. Pat. Nos. 5,312,940, 5,969,170 and 6,111,121, which are incorporated herein by reference. While they catalyze a considerable number of olefin metathesis transformations, these bisphosphine complexes can exhibit lower activity than desired.

Second-generation metathesis catalysts with greatly increased activity have now been prepared by replacing one of the phosphine ligands with an N-heterocyclic carbene (NHC) ligand to give complexes of the general formula (L)(PR₃)(X)₂Ru═CHR^(a) wherein L represents an NHC ligand such as 1,3-dimesitylimidazole-2-ylidene (IMES) and 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene (sIMES), X represents a halogen (e.g., Cl, Br, or I), R represents an alkyl, cycloalkyl, or aryl group (e.g., butyl, cyclohexyl, or phenyl), and R^(a) represents an alkyl, alkenyl, or aryl group (e.g., methyl, CH═CMe₂, phenyl, etc.). Examples of these types of NHC ligands and catalysts are described in PCT publications WO 99/51344 and WO 00/71554, which are incorporated herein by reference. Further examples of the synthesis and reactivity of some of these active ruthenium complexes are reported by A. Fürstner, L. Ackermann, B. Gabor, R. Goddard, C. W. Lehmann, R. Mynott, F. Stelzer, and O. R. Thiel, Chem. Eur. J., 2001, 7, No. 15, 3236-3253; Blackwell H. E., O'Leary D. J., Chatterjee A. K., Washenfelder R. A., Bussmann D. A., Grubbs R. H. J. Am. Chem. Soc. 2000, 122, 58-71; Chattetjee A. K., Morgan J. P., Scholl M., Grubbs R. H. J. Am. Chem. Soc. 2000, 122, 3783-3784; Chatterjee A. K., Grubbs R. H. Angew. Chem. Int. Ed. 2002, 41, 3171-3174; Chatterjee A. K., Choi T. L., Sanders D. P., Grubbs R. H. J. Am. Chem. Soc. 2003, 125, 11360-11370. The disclosure of these articles are incorporated herein by reference.

Despite such advances in the development of olefin metathesis catalysts, the metathesis of hindered olefins remains difficult and certain metathesis reactions to form tetra-substituted olefins proceed slowly and in low to moderate yields. A need exists, therefore, for metathesis catalysts capable of efficiently and effectively carrying out metathesis reactions with hindered olefins. The ruthenium catalysts of this invention answer that need.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the organometallic complexes, methods and reaction systems herein disclosed will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

FIG. 1 shows a reaction scheme illustrating an exemplary embodiment of the method for preparing a cyclic tetra-substituted olefin via ring-closing metathesis herein disclosed.

FIG. 2 shows a diagram illustrating the results of a ring-closing metathesis of 1 with catalysts 6 a, 6 b, 6 c and A (referred to as C848 in graph), reported in Example 3 and in particular in Tables 3 to 6.

FIG. 3 shows a diagram illustrating the results of a ring-closing metathesis of 1 with catalysts 7 a, 7 b, 7 c, reported in Example 3 and in particular in Tables 9 to 11.

FIG. 4 depicts the single crystal X-ray structure was obtained for catalyst 12 described in Example 7.

FIG. 5 is a graph of the conversion over time for the ring-closing metathesis of 1 with catalyst 12, described in Example 8.

FIG. 6 is a graph of the conversion over time for the ring-closing metathesis of 1 with catalyst 12 in C₆D₆, described in Example 8.

FIG. 7 is a graph of the conversion over time for the ring-closing metathesis of 13 with catalyst 12 described in Example 9.

FIG. 8 is a graph of the conversion over time for the ring-closing metathesis of 15 with catalyst 12 described in Example 9.

FIG. 9 shows the graph of conversion over time for the ring-closing metathesis of 1 with catalyst 24 described in Example 19.

FIG. 10 is a graph of conversion over time for the ring-closing metathesis of 1 with catalyst 24 in C₆D₆, described in Example 19.

FIG. 11 is a graph of conversion over time for the ring-closing metathesis of 13 with catalyst 24 described in Example 20.

FIG. 12 is a graph of the conversion over time for the ring-closing metathesis of 15 with catalyst 24 described in Example 20.

FIG. 13 is a graph of conversion over time for the ring-closing metathesis of 1 with catalyst 25 described in Example 21.

FIG. 14 is a graph of the conversion over time for the ring-closing metathesis of 1 with catalyst 25 in C₆D₆ described in Example 21.

FIG. 15 is a graph of the conversion over time for the ring-closing metathesis of 13 with catalyst 25 described in Example 22.

FIG. 16 is a graph of conversion over time for the ring-closing metathesis of 15 with catalyst 25 described in Example 22.

FIG. 17 is a graph of the conversion over time for the ring-closing metathesis of 1 with catalyst 26 described in Example 23.

FIG. 18 shows the conversion over time for the ring-closing metathesis of 1 with catalyst 6 a, 6 c, 27 a and 27 c described in Example 24.

FIG. 19 shows the conversion over time for the ring-closing metathesis of 1 with catalyst 6 a and 7 a in toluene described in Example 25.

FIG. 20 is a graph of the conversion over time for the RCM reaction of 15 in Example 29 for catalyst 6 a.

FIG. 21 is a graph of the conversion over time for the RCM reaction of 13 in Example 29 for catalyst 6 a.

FIG. 22 is a graph of the conversion over time for the RCM reaction of 15 in Example 29 for catalyst 7 a.

FIG. 23 is a graph of the conversion over time for the RCM reaction of 13 in Example 29 for catalyst 7 a.

SUMMARY OF THE INVENTION

The invention relates to ruthenium alkylidene complexes having an N-heterocyclic carbene ligand comprising a 5-membered heterocyclic ring having a carbenic carbon atom and at least one nitrogen atom contained within the 5-membered heterocyclic ring, wherein the nitrogen atom is directly attached to the carbenic carbon atom and is substituted by a phenyl ring, and wherein the phenyl ring has a hydrogen at either or both ortho positions and is substituted at least one ortho-, or meta-position.

In a preferred embodiment, the invention relates to N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst of formula (I):

The catalysts of formula (I) contain the NHC ligand as well as the other ligands shown. In formula (I), X¹ and X² are independently anionic ligands; “n” is 0, 1, or 2; R⁹ and R¹⁰ are each independently hydrogen or a substituted or unsubstituted substituent selected from the group consisting of C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, C₂-C₂₀ alkynyl, aryl, C₁-C₂₀ carboxylate, C₁-C₂₀ alkoxy, C₂-C₂₀ alkenyloxy, C₂-C₂₀ alkynyloxy, aryloxy, C₂-C₂₀ alkoxycarbonyl, C₁-C₂₀ alkylthio, C₁-C₂₀ alkylsulfonyl and C₁-C₂₀ alkylsulfinyl; L is a neutral 2-electron donor ligand; and “m” is 1 or 2. R⁹ and R¹⁰ may optionally be linked together to form a cyclic structure via one of the substituents mentioned above. L may optionally be linked to R¹⁰ to form a chelating carbene ligand, however, the formation of the chelating carbene ligand only occurs when n is 0. When “m” is a heteroarene ligand. Preferably, the heteroarene ligand 2, L is pyridine or substituted pyridine, which forms a (bis)pyridine catalyst. See Example 28, depicting a (bis)pyridine catalyst.

Preferred NHC ligands for the ruthenium catalysts of the invention are those of formulas (II)-(V):

In formulas (II)-(V), R¹, R², and R³ are either:

-   -   a) each R¹ is independently a primary or secondary C₁-C₄ alkyl         group; each R² is independently H, a substituted or         unsubstituted C₁-C₁₀ alkyl group, substituted or unsubstituted         phenyl, substituted or unsubstituted naphthyl, or substituted or         unsubstituted anthracenyl; and each R³ is independently H, a         substituted or unsubstituted C₁-C₈ alkyl group, substituted or         unsubstituted phenyl, substituted or unsubstituted naphthyl, or         substituted or unsubstituted anthracenyl, or a functional group         selected from the group consisting of halo, hydroxyl,         sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso,         sulfo, sulfonato, boryl, borono, phosphono, phosphonato,         phosphinato, phospho, phosphino, and silyloxy; or     -   b) R¹ is H; each R² is independently H, a substituted or         unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted         phenyl, substituted or unsubstituted naphthyl, or substituted or         unsubstituted anthracenyl; and R³ is independently H, a         substituted or unsubstituted C₁-C₈ alkyl group, substituted or         unsubstituted phenyl, substituted or unsubstituted naphthyl, or         substituted or unsubstituted anthracenyl or a functional group         selected from the group consisting of halo, hydroxyl,         sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso,         sulfo, sulfonato, boryl, borono, phosphono, phosphonato,         phosphinato, phospho, phosphino, and silyloxy; with the provisos         that both R² substituents on the same phenyl ring are not H.         R⁴ and R⁶ are each independently H, a substituted or         unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted         aryl, or in formulas (III) and (V) together with the carbons         carrying them form a substituted or unsubstituted, fused 4-8         membered carbocylic ring or a substituted or unsubstituted,         fused aromatic ring, preferably a fused phenyl ring. R⁵ and R⁷         are independently H, a substituted or unsubstituted C₁-C₈ alkyl         group. R⁸ is a C₁-C₁₂ alkyl or a C₃-C₁₂ cycloalkyl.

Another embodiment of the invention relates to an olefin metathesis reaction which contacts an olefin with an N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst of the invention under metathesis conditions. The catalysts of the invention may be used in, for example, ring-closing metathesis (RCM), cross metathesis (CM), ring-opening metathesis polymerization (ROMP), and acyclic diene metathesis polymerization (ADMET).

A further embodiment of the invention relates to the preparation of tetra-substituted cyclic olefins via a ring-closing metathesis. In this embodiment, the invention provides a ring-closing metathesis method to prepare a tetra-substituted cyclic olefin. In the method, an olefinic compound having at least two terminal olefins which are substituted at the beta-carbon of each terminal olefin is contacted with an N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst of the invention under metathesis conditions to form a cyclic tetra-substituted olefin.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalysts. Advantageously, the catalysts of the invention display greater efficiency/activity than current olefin metathesis catalysts for catalyzing ring-closing metathesis (RCM) reactions to form tetra-substituted cyclic olefins. The catalysts also perform the other known metathesis reactions in the family of metathesis reactions discussed above. The catalysts are also particularly useful in cross-metathesis to prepare tri-substituted olefins, and di-substituted olefins that are further substituted at the allylic carbon. The N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalysts of the invention have the following general formula (I):

In the catalysts of formula (I), X¹ and X² are independently anionic ligands. Preferably, X¹ and X² are halide, or one of the following groups: C₁-C₂₀ alkyl, aryl, C₁-C₂₀ alkoxide, aryloxide, C₃-C₂₀ alkyldiketonate, aryldiketonate, C₁-C₂₀ carboxylate, arylsulfonate, C₁-C₂₀ alkylsulfonate, C₁-C₂₀ alkylthio, C₁-C₂₀ alkylsulfonyl, or C₁-C₂₀ alkylsulfinyl. Optionally, X¹ and X² may be substituted with one or more moieties selected from the group consisting of C₁-C₁₀ alkyl, C₁-C₁₀ a alkoxy, and aryl which in turn may each be further substituted with one or more groups selected from halogen, C₁-C₅ alkyl, C₁-C₅ alkoxy, and phenyl. In more preferred embodiments, X¹ and X² are halide, benzoate, C₁-C₅ carboxylate, C₁-C₅ alkyl, phenoxy, C₁-C₅ alkoxy, C₁-C₅ alkylthio, aryl, and C₁-C₅ alkyl sulfonate. As discussed below, the other ligands in a catalyst of the invention, when substituted, may also contain such substituents. In even more preferred embodiments, X¹ and X² are each halide, CF₃ CO₂, CH₃,CO₂, CFH₂ CO₂, (CH₃)₃CO, (CF₃)₂ (CH₃)CO, (CF₃)(CH₃)₂CO, PhO, MeO, EtO, tosylate, mesylate, or trifluoromethanesulfonate. In the most preferred embodiments, X¹ and X² are each chloride.

The variable “n” defines the number of successive double bounds in the alkylidene substituted by R⁹ and R¹⁰. The variable “n” is 0, 1 or 2. Preferably, “n” is 0.

R⁹ and R¹⁰ are each independently hydrogen or a substituted or unsubstituted group selected from the group consisting of C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, C₂-C₂₀ alkynyl, aryl, C₁-C₂₀ carboxylate, C₁-C₂₀ alkoxy, C₂-C₂₀ alkenyloxy, C₂-C₂₀ alkynyloxy, aryloxy, C₂-C₂₀ alkoxycarbonyl, C₁-C₂₀ alkylthio, C₁-C₂₀ 20 alkylsulfonyl and C₁-C₂₀ alkylsulfinyl. Optionally, each of the R⁹ or R¹⁰ substituent group may be substituted with one or more moieties selected from the group consisting of C₁-C₁₀ alkyl, C₁-C₁₀ alkoxy, and aryl which in turn may each be further substituted with one or more groups selected from a halogen, a C₁-C₅ alkyl, C₁-C₁₅ alkoxy, and phenyl. Moreover, R⁹ and R¹⁰, as well as any other of the catalyst ligands, may further include one or more functional groups as long as they do not defeat the activity of the catalyst. Examples of suitable functional groups include but are not limited to: hydroxyl, thiol, thioether, ketone, aldehyde, ester, ether, amine, imine, amide, nitro, carboxylic acid, disulfide, carbonate, isocyanate, carbodiimide, carboalkoxy, carbamate, and halogen. R⁹ and R¹⁰ may optionally be linked together to form a cyclic structure via one of the substituents mentioned above.

In preferred embodiments of these catalysts, the R⁹ substituent is hydrogen, C₁-C₅ alkyl or aryl and the R¹⁰ substituent is selected from the group consisting of C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, and aryl. In even more preferred embodiments, the R¹⁰ substituent is phenyl or vinyl, optionally substituted with one or more moieties selected from the group consisting of C₁-C₅ alkyl, C₁-C₅ alkoxy, phenyl, and a functional group. In especially preferred embodiments, R¹⁰ is phenyl or vinyl substituted with one or more moieties selected from the group consisting of chloride, bromide, iodide, fluoride, —NO₂, —NMe₂, methyl, methoxy and phenyl. In the most preferred embodiments, the R¹⁰ substituent is phenyl or —C═C(CH₃)₂.

L may be any neutral 2-electron donor ligand known in the art. The variable “m” defines the number of neutral donor ligands, L. The variable “m” is 1 or 2 and preferably 1. When “m” is 1, L is any neutral 2-electron donor ligand. L may be linked to R¹⁰ forming a chelating carbene ligand when “n” is zero. When “m” is 2, L is a heteroarene ligand such as pyridine or substituted pyridine. See U.S. Pat. Nos. 6,759,537 and 6,818,586, herein incorporated by reference in their entirety; for examples of suitable heteroarene ligands. Preferably, the heteroarene ligand is pyridine or substituted pyridine.

In a preferred embodiment, L is selected from the group consisting of phosphine, sulfonated phosphine, phosphite, phosphinite, phosphonite, arsine, stibine, ether, amine, amide, imine, sulfoxide, carboxyl, nitrosyl, pyridine, and thioether. In more preferred embodiments, L is a phosphine of the formula PR′R″R′″, where R′, R″, and R′″ are each independently aryl; C₁-C₁₀ alkyl (in particular, a primary or secondary alkyl); or C₃-C₆ cycloalkyl. In the most preferred embodiments, L is selected from the group consisting of P(cyclohexyl)₃, P(cyclopentyl)₃, P(isopropyl)₃, and P(phenyl)₃.

In a preferred embodiment, L may be linked to R¹⁰ forming a chelating carbene ligand. When forming a chelating carbene ligand, n is zero. The L portion of the chelating carbene ligand is still a 2-electron donor ligand when linked to R¹⁰. L may or may not be linked to R¹⁰ through a spacer moiety. U.S. Pat. No. 6,921,735 describes chelating carbene ligands and is incorporated herein by reference for examples of how the ligand and R substituent on the carbene can be linked through various spacer moieties. The spacer moiety may be substituted or unsubstituted. Preferred catalysts of the invention where L and R¹⁰ are linked include the following:

Examples of ruthenium complexes with chelating carbene ligands, ligands linking the L ligand and the R¹⁰ substitutent, are also described in Kingsbury, J. S.; Harrity, J. P. A.; Bonitatebus, P. J., Jr.; Hoveyda, A. H. J. Am. Chem. Soc. 1999, 121, 791 and Garber, S. B.; Kingsbury, J. S.; Gray, B. L.; Hoveyda, A. H. J. Am. Chem. Soc. 2000, 122, 8168. Preferably, R¹⁰ is linked to L via spacer group being 2-5 atoms in length between L and R¹⁰, for example via an alkyl group, a cycloloalkyl group, or an aryl group. A preferred spacer group is a substituted or unsubstituted phenyl group.

In the catalysts of the invention there is an N-heterocyclic carbene (NHC) ligand which is a ligand comprising a 5-membered NHC ring, i.e., a carbene where the carbenic carbon atom is contained within a 5-membered cyclic structure. The 5-membered cyclic structure that contains the carbenic carbon atom also contains at least one nitrogen atom directly attached to the carbenic carbon atom and that nitrogen atom is substituted by a phenyl ring. The phenyl ring itself has a hydrogen (i.e. is unsubstituted) at either or both ortho positions but substituted at least one ortho-, or meta-position.

As described in the preferred embodiments below, the 5-membered NHC ring may, in some circumstances, be part of a polycyclic group and the phenyl ring may be part of a polycyclic aryl group. Preferred NHC ligands are those of those of formulas (II)-(V):

In the preferred NHC ligands of formulas (II)-(V) there are two preferred combinations of R¹, R², and R³ which define the substitution pattern on the phenyl ring bound to the nitrogen atom bound to the carbene carbon. Note that in the NHC ligands used in the complexes of the invention, at least one ortho position on the phenyl ring is a hydrogen. In other words, the phenyl ring is always unsubstitued at least one ortho position. In certain preferred combinations of R¹, R², and R³ both ortho positions are hydrogen and, therefore, unsubstituted. The preferred combinations of R¹, R², and R³ are:

-   -   a) each R¹ is independently a primary or secondary C₁-C₄ alkyl         group; each R² is independently H, a substituted or         unsubstituted C₁-C₁₀ alkyl group, substituted or unsubstituted         phenyl, substituted or unsubstituted naphthyl, or substituted or         unsubstituted anthracenyl; and each R³ is independently H, a         substituted or unsubstituted C₁-C₈ alkyl group, substituted or         unsubstituted phenyl, substituted or unsubstituted naphthyl, or         substituted or unsubstituted anthracenyl, or a functional group         selected from the group consisting of halo, hydroxyl,         sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso,         sulfo, sulfonato, boryl, borono, phosphono, phosphonato,         phosphinato, phospho, phosphino, and silyloxy; or     -   b) R¹ is H; each R² is independently H, a substituted or         unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted         phenyl, substituted or unsubstituted naphthyl, or substituted or         unsubstituted anthracenyl; and R³ is independently H, a         substituted or unsubstituted C₁-C₈ alkyl group, substituted or         unsubstituted phenyl, substituted or unsubstituted naphthyl, or         substituted or unsubstituted anthracenyl or a functional group         selected from the group consisting of halo, hydroxyl,         sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso,         sulfo, sulfonato, boryl, borono, phosphono, phosphonato,         phosphinato, phospho, phosphino, and silyloxy; with the proviso         that both R² substituents on the same phenyl ring are not H.

In combination a), R¹ is preferably methyl, ethyl, or iso-propyl. Each separate R² is preferably H, iso-butyl, tert-butyl, neopentyl, neohexyl, or phenyl and is most preferably H. Each R³ is preferably H, iso-butyl, tert-butyl, neopentyl, neohexyl, or phenyl and is most preferably H.

In combination b), when R¹ and R³ are H and R² is one of the listed substituents, the phenyl group of the NHC ligand is bis-meta substituted; and when R¹ and R³ and R² are each one of the listed substituents, the phenyl group of the NHC ligand is bis-meta and para-substituted. Because R¹ is H, the proviso within combination b), that both R²'s on the same phenyl ring are H, exclude those NHC ligands having an unsubstituted phenyl or a, para-substituted phenyl. R² is preferably a secondary or tertiary C₃-C₁₀ alkyl or aryl; more preferably, iso-butyl, tert-butyl, neopentyl, neohexyl, or phenyl and most preferably tert-butyl. R³ is preferably H, iso-butyl, tert-butyl, neopentyl, neohexyl, or phenyl and is most preferably H.

In the NHC ligands used in the complexes of the invention, R⁴ and R⁶ are each independently H, a substituted or unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted aryl, or in formulas (III) and (V), together with the carbons carrying them, form a substituted or unsubstituted, fused 4-8 membered carbocylic ring or a substituted or unsubstituted, fused aromatic ring. Preferably R⁴ and R⁶ are H, C₁-C₄ alkyl, or fused cyclolhexyl or phenyl (in formulas (III) and (V)). R⁵ and R⁷ are independently H, a substituted or unsubstituted C₁-C₈ alkyl group and preferably H or C₁-C₄ alkyl.

In the NHC ligands of formulas (IV) and (V), R⁸ is a C₁-C₁₂ alkyl or a C₃-C₁₂ cycloalkyl. Preferably R⁸ is methyl, ethyl, or iso-propyl and most preferably is methyl.

Examples of preferred NHC ligands for catalysts of the invention are shown below:

where R¹=methyl, ethyl, propyl, isopropyl

where R¹=methyl, ethyl, propyl, isopropyl

-   -   where R²=tert-butyl

-   -   where R²=tert-butyl

where R¹=methyl, ethyl, propyl, isopropyl; R⁶=R⁷=hydrogen or methyl; and R⁸=methyl.

where R¹=methyl, ethyl, propyl, isopropyl; and R⁸=methyl. Synthesis of NHC Ligands

The NHC ligands of formulas (II) and (III) used to form the catalysts of the invention may be prepared from aniline derivatives using known procedures used to prepare other known NHC ligands, such as the second generation metathesis catalysts discussed above. The aniline derivative used bears the desired substituents and substitution pattern. Typically, two equivalents of the aniline derivative are reacted with glyoxal to begin the synthesis. Use of the two equivalents of the same aniline gives a symmetric NHC ligand. Asymmetric NHC ligands can be prepared by using two different aniline derivatives. For asymmetric NHC ligands, the aniline derivatives are preferably reacted with the glyoxal in two separate steps to avoid a mixture of products.

Alternatively, NHC ligands of formulas (II) and (III) maybe prepared by reacting two equivalents of the same aniline with oxalyl chloride. Subsequent reduction of the product bisamide yields a diamine that can be transformed by techniques known in the art to a salt, which is a direct NHC ligand precursor. For differentially substituted NHC ligands, typically, one aniline is reacted with ethyl chlorooxoacetate and the product of that reaction is reacted with the second aniline. Again, reduction of the product bisamide yields a diamine that can be transformed by techniques known in the art to a salt, which is a direct NHC ligand precursor. Examples of the preparation of NHC ligands of formulas (II) and (III) are shown below in Examples 1, 6, 12, 13, and 17.

Salt precursors of NHC ligands of formulas (IV) and (V) can be prepared by a procedure similar to that described by Blechert and coworkers in Organometallics 2006, 25, 25-28: first a diamine R⁸NH—(CH₂)₂—NH₂ is arylated under Buchwald-Hartwig conditions to give R⁸NH—(CH₂)₂—NH[C₆HR¹(R²)₂R³], which is then reacted with triethylorthoformate in the presence of NH₄BF₄ to give the HBF₄ salt precursor of NHC ligands of formula (IV). Salt precursors of NHC ligands of formula (V) can be prepared by reacting N-(substituted phenyl)imidazole (where substituted phenyl is C₆HR¹(R²)₂R³) with an alkyl halide (where alkyl is R⁸) according to the procedure described by Fürstner and coworkers in Organometallics 2004, 23, 280-287. The NHC ligands of formulas (IV) and (V) may be prepared by deprotonation of their corresponding NHC salts.

Synthesis of Catalysts

The ruthenium catalysts of the invention may be prepared using methods known in the art. In general, the catalysts of the present invention are prepared via a ligand exchange reaction, for example, by substituting an NHC ligand for one of the neutral electron donor ligands in a first generation ruthenium carbene complexes (discussed above). For example, a catalyst of the invention can be prepared by replacing a phosphine ligand in a complex of the general formula (PR₃)₂(X)₂Ru═CHR with an NHC ligand described above. As discussed in the Background of the Invention, these synthetic procedures are known in the art. Examples 2, 7, 11, 12, 14, and 15 illustrate preparation of ruthenium catalysts of the invention by this method.

Metathesis Reactions

The ruthenium catalysts of the invention are particularly efficient olefin metathesis catalysts. Accordingly, one embodiment of the invention is an olefin metathesis reaction which contacts an olefin with an N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst of the invention under metathesis conditions. The catalysts of the invention may be used in, for example, ring-closing metathesis (RCM), cross metathesis (CM), self metathesis (which is a type of cross metathesis), ring-opening metathesis polymerization (ROMP), and acyclic diene metathesis polymerization (ADMET).

The metathesis conditions for the catalysts of the invention are the same as those used in other olefin metathesis reactions and with other known olefin metathesis catalysts. Generally speaking, the olefin metathesis reactions are run at a temperature ranging from about 10° C. to about 70° C. and for a time period ranging from about 5 minutes to about 24 hours. The catalysts of the invention may be used in the same amounts as know for other olefin metathesis catalysts. Typically, about 1 to about 10 mol % of the catalyst is used and more often about 5 mol %.

The ruthenium catalysts of the invention are particularly useful in metathesis reactions for the production of tetra-substituted cyclic olefins. The catalysts of the invention have significantly increased efficiency/activity for the preparation of tetra-substituted cyclic olefins via olefin metathesis. To answer the need for more efficient preparation of such olefins another embodiment of the invention is a ring-closing metathesis method to prepare a tetra-substituted cyclic olefin. The method contacts an olefinic compound having at least two terminal olefins which are substituted at the beta-carbon of each terminal olefin with an N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst of the invention under metathesis conditions to form a cyclic tetra-substituted olefin.

A preferred group of olefinic compounds are those which have a structure according to formula (VI):

In formula (VI), Q is selected from hydrocarbylene, substituted hydrocarbylene, heteroatom-containing hydrocarbylene, and substituted heteroatom-containing hydrocarbylene. Q¹ and Q² are independently selected from hydrogen, hydrocarbyl, substituted hydrocarbyl, heteroatom-containing hydrocarbyl, substituted heteroatom-containing hydrocarbyl, and other groups such as halide, hydroxyl, sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso, sulfo, sulfonato, boryl, borono, phosphono, phosphonato, phosphinato, phospho, phosphino, and silyloxy. In the preparation of hindered cyclic olefins, both Q¹ and Q² cannot both be hydrogen and, more preferably, are both not hydrogen.

The catalysts are useful in cross-metathesis to prepare tri-substituted olefins, and di-substituted olefins which are further substituted at the allylic carbon. Accordingly, an embodiment of the invention relates to a cross-metathesis reaction in which an N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst of the invention contacts two olefins under metathesis conditions. The first olefin is monosubstituted at the β-carbon and either unsubstituted or monosubstituted at the ∝-carbon. The second olefin is either disubstituted at the β-carbon or monosubstituted at the β-carbon but also has further substitution at the allylic carbon. Both olefins are either monosubstituted or unsubstituted at the ∝-carbon.

Examples of tri-substituted olefins are those having the formula Q¹Q²C═CHQ³. Q¹, Q², and Q³ are independently selected from hydrocarbyl, substituted hydrocarbyl, heteroatom-containing hydrocarbyl, substituted heteroatom-containing hydrocarbyl, and other groups such as halide, hydroxyl, sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso, sulfo, sulfonato, boryl, borono, phosphono, phosphonato, phosphinato, phospho, phosphino, and silyloxy. Any number of Q¹, Q², and Q³ may also be linked as part of a cyclic olefin.

Di-substituted olefins are represented, for example, by the formula Q¹Q²C═CH₂ or Q¹HC═CHQ². Q¹ and Q² are independently selected from hydrocarbyl, substituted hydrocarbyl, heteroatom-containing hydrocarbyl, substituted heteroatom-containing hydrocarbyl, and other groups such as halide, hydroxyl, sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso, sulfo, sulfonato, boryl, borono, phosphono, phosphonato, phosphinato, phospho, phosphino, and silyloxy. Q¹ and Q² may also be linked in the case of cyclic olefins.

The formula Q¹HC═CHCQ²Q³Q⁴ is representative of exemplary di-substituted olefins having further substitution at the allylic carbon. In this formula Q¹, Q², Q³, and Q⁴ are independently selected from hydrogen, hydrocarbyl, substituted hydrocarbyl, heteroatom-containing hydrocarbyl, substituted heteroatom-containing hydrocarbyl, and other groups such as halide, hydroxyl, sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso, sulfo, sulfonato, boryl, borono, phosphono, phosphonato, phosphinato, phospho, phosphino, and silyloxy, provided that at least two of Q², Q³ and Q⁴ are different from hydrogen. Q¹, Q², Q³, and Q⁴ can be linked when the olefin is a cyclic olefin.

The term “hydrocarbyl” refers to univalent hydrocarbyl radicals containing 1 to about 30 carbon atoms, preferably 1 to about 24 carbon atoms, most preferably 1 to about 12 carbon atoms, including linear, branched, cyclic, saturated and unsaturated species, such as alkyl groups, alkenyl groups, aryl groups, and the like. The term “lower hydrocarbyl” intends a hydrocarbyl group of 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, and the term “hydrocarbylene” intends a divalent hydrocarbyl moiety containing 1 to about 30 carbon atoms, preferably 1 to about 24 carbon atoms, most preferably 1 to about 12 carbon atoms, including linear, branched, cyclic, saturated and unsaturated species. The term “lower hydrocarbylene” intends a hydrocarbylene group of 1 to 6 carbon atoms. “Substituted hydrocarbyl” refers to hydrocarbyl substituted with one or more substituent groups such as discussed above, and the terms “heteroatom-containing hydrocarbyl” and “heterohydrocarbyl” refer to hydrocarbyl in which at least one carbon atom is replaced with a heteroatom. Similarly, “substituted hydrocarbylene” refers to hydrocarbylene substituted with one or more substituent groups discussed above, and the terms “heteroatom-containing hydrocarbylene” and “heterohydrocarbylene” refer to hydrocarbylene in which at least one carbon atom is replaced with a heteroatom. Unless otherwise indicated, the term “hydrocarbyl” and “hydrocarbylene” are to be interpreted as including substituted and/or heteroatom-containing hydrocarbyl and hydrocarbylene moieties, respectively.

EXAMPLES Example 1 Ortho Substituted NHC Ligand Synthesis

General procedure for the preparation of N,N′-Diaryl oxamides. Oxalyl chloride (4.36 mL, 50 mmol) was added dropwise to a stirred solution of aniline C₆H₄RNH₂ (100 mmol, 2 equiv) and base (100 mmol, 2 equiv) in THF (200 mL) at 0° C. Triethylamine or aq. NaOH may be used as bases for this reaction. Upon addition, the reaction was allowed to warm up to room temperature (r.t.) and stirred for 1 h. The reaction mixture was then concentrated in vacuo and diluted with water (100 mL). The white precipitate was collected by filtration, washed with dilute HCl (100 mL), water (2×100 mL), and dried in vacuo. The following N,N′-diaryl oxamides were prepared by this procedure:

N,N′-Bis(o-tolyl) oxamide. Obtained in a 98% yield as a white solid. ¹H NMR (300 MHz, CDCl₃): δ 9.38 (s, 2H), 8.09 (d, ³J_(HH)=7.8 Hz, 2H), 7.31-7.12 (m, 6H), 2.39 (s, 6H).

N,N′-Bis(2-ethylphenyl)oxamide. Obtained in a 71% yield as a white solid.

N,N′-Bis(2-isopropylphenyl)oxamide. Obtained in a 60% yield as a white solid. ¹H NMR (300 MHz, CDCl₃): δ 9.52 (s, 2H), 8.05 (d, ³J_(HH)=6.9 Hz, 2H), 7.36-7.21 (m, 6H), 3.16 (m, 2H), 1.32 (d, ³J_(HH)=6.6. Hz, 12H), 0.98 (d, ³J_(HH)=6.9 Hz, 12H).

General procedure for the preparation of N,N′-Diarylethylenediamine hydrochloride 3. Borane-tetrahydrofuran complex (1M solution in THF, 125 mL, 6.25 equiv) was added dropwise with stirring to oxamide (20 mmol) at r.t. The reaction mixture was refluxed overnight, allowed to cool to r.t. and excess borane was quenched by careful, dropwise addition of water until no more gas evolution was observed. The reaction mixture was concentrated in vacuo, extracted with ether and the organic extracts were dried over Na₂SO₄. 2M HCl in ether (30 mL, 3 equiv) was then added to the dry organic extracts and the resulting white precipitate was collected by filtration, washed with a small amount of ethanol and dried in vacuo. The following N,N′-diarylethylenediamine hydrochlorides were prepared by this procedure:

N,N′-Bis(o-tolyl)ethylenediamine hydrochloride 3a (i.e. compound 3 wherein R=methyl). Obtained in a 89% yield as a white solid. ¹H NMR (300 MHz, D₂O): δ 7.30-7.10 (m, 8H), 3.67 (s, 4H), 2.45 (s, 6H).

N,N′-Bis(2-ethylphenyl)ethylenediamine hydrochloride 3b (i.e. compound 3 wherein R=ethyl). Obtained in a 74% yield as a white solid.

N,N′-Bis(2-isopropylphenyl)ethylenediamine hydrochloride 3c (i.e. compound 3 wherein R=isopropyl). Obtained in a 91% yield as a white solid. ¹H NMR (300 MHz, D₂O): δ 7.33 (d, ³J_(HH)=6.9 Hz, 2H), 7.15 (m, 4H), 6.98 (d, ³J_(HH)=6.9 Hz, 2H), 3.51 (s, 4H), 2.74 (m, 2H), 0.98 (d, ³J_(HH)=6.9 Hz, 12H).

General procedure for the preparation of NHC ligand precursor 4 or Dihydroimidazolium salt 4. Triethyl orthoformate (150 mL) was added to the diamine hydrochloride 3 in a 250-mL r.b. flask. The flask was equipped with a distillation head and heated for about 1 h, during which ethanol distilled over at 78-80° C., followed by about 70 mL of triethyl orthoformate at 135-140° C. The reaction mixture was then allowed to cool to r.t., diluted with hexanes and the white precipitate was collected by filtration, washed with hexanes and ether and dried in vacuo. The following dihydroimidazolium salts were prepared by this procedure:

1,3-Bis(o-tolyl)-4,5-dihydroimidazolium chloride 4a (i.e. compound 4 wherein R=methyl). Obtained in a 93% yield as a white solid. ¹H NMR (300 MHz, CDCl₃): δ 8.83 (s, 1H), 7.78-7.21 (d, 8H), 4.64 (s, 4H), 2.43 (s, 6H).

1,3-Bis(2-ethylphenyl)-4,5-dihydroimidazolium chloride 4b (i.e. compound 4 wherein R=ethyl). Obtained in a 74% yield as a white solid. ¹H NMR (300 MHz, CD₂Cl₂) δ 9.04 (1H, s), 7.92 (2H, d, J=7.5 Hz), 7.47-7.30 (6H, m), 4.64 (4H, s), 2.78 (4H, q, J=7.8 Hz), 1.31 (6H, t, J=7.8 Hz).

1,3-Bis(2-isopropylphenyl)-4,5-dihydroimidazolium chloride 4c (i.e. compound 4 wherein R=isopropyl). Obtained in an 84% yield as a white solid. ¹H NMR (300 MHz, CDCl₃): δ 8.22 (d, ³J_(HH)=7.2 Hz, 2H), 8.04 (s, 1H), 7.34 (m, 6H), 4.73 (s, 4H), 3.06 (m, 2H), 1.29 (d, ³J_(HH)=6.0 Hz, 12H).

Example 2 Catalyst Synthesis

General procedure for the preparation of ortho-substituted catalyst 6. Potassium bis(trimethylsilyl)amide (1.4 g, 7.0 mmol, 1.23 equiv) was added to a suspension of dihydroimidazolium salt 4 (compound 4 of reaction scheme 3) (2.3 g, 6.7 mmol, 1.15 equiv) in toluene (57 mL) under argon. The reaction mixture was stirred at r.t. for 30 min, then compound 5 (4.7 g, 5.7 mmol) was added and stirring was continued for 1.5 h at r.t. The reaction mixture was then concentrated and catalyst 6 was isolated by column chromatography and dried in vacuo. The ortho-substituted catalysts were prepared by this procedure:

Catalyst 6a (i.e. compound 6 wherein R=methyl). Obtained in a 66% yield after column chromatography on silica gel (unreacted 5 was first eluted with 1:9 EtOAc-hexanes, then 6a was eluted with 1:3 EtOAc-hexanes). Brown crystalline solid. ¹H NMR (300 MHz, C₆D₆): δ 19.61 (s), 8.70 (br), 7.64 (br), 7.31-6.76 (m), 6.59 (m), 6.34 (br), 3.53-3.01 (m), 2.62 (s), 2.20-2.04 (br), 1.67-1.06 (m). ³¹P NMR (121 MHz, C₆D₆): δ 27.87 (s), 25.15 (s).

Catalyst 6b (i.e., compound 6 wherein R=ethyl) Obtained in a 60% yield after column chromatography on silica gel (unreacted 5 was first eluted with 1:9 EtOAc-hexanes, then 6a was eluted with 1:3 EtOAc-hexanes). Brown crystalline solid. ¹H NMR (300 MHz, C₆D₆): δ 19.59 (s), 8.74-8.62 (m), 8.25 (br), 7.71 (br), 7.34-6.85 (m), 6.67 (br), 6.44 (br), 3.55-3.07 (m), 2.79-2.19 (m), 1.69-0.91 (m), 1.67-1.06 (m). ³¹P NMR (121 MHz, C₆D₆): δ 25.75 (s), 25.04 (s).

Catalyst 6c (i.e. compound 6 wherein R=isopropyl). Obtained in a 68% yield after column chromatography on silica gel (unreacted 5 was first eluted with 1:10 EtOAc-hexanes, then 6c was eluted with 1:3 EtOAc-hexanes). Brown crystalline solid. ¹H NMR (300 MHz, C₆D₆): δ 19.68 (s), 19.49 (s), 8.93-8.87 (m), 8.30 (b), 7.60 (d), 7.34-7.12 (m), 6.97 (t), 6.80 (d), 6.70-6.44 (m), 3.85-3.08 (m), 2.22-2.12 (q), 2.02-1.91 (q), 1.66-0.97 (m). ³¹P NMR (121 MHz, C₆D₆): δ 26.33 (s), 23.92 (s).

General procedure for the preparation of ortho-substituted Catalyst 7. 2-Isopropoxy-β-methylstyrene (0.89 g, 5.1 mmol, 2 equiv) was added to a solution of catalyst 6 (2.1 g, 2.5 mmol) in CH₂Cl₂ (25 mL). The reaction mixture was refluxed for 1 h, then 2N HCl in methanol (1.8 mL, 3.6 mmol, 1.5 equiv) was added and the mixture was refluxed for another 1 h, then evaporated to dryness in vacuo. The residue was dissolved in a minimal amount of CH₂Cl₂ and catalyst 7 was precipitated by addition of pentane. It was collected by filtration and dried in vacuo. The following ortho-substituted catalysts were prepared by this procedure:

Catalyst 7a (i.e., compound 7 wherein R=methyl). Obtained in a 71% yield after column chromatography on silica gel (eluted with 1:5 EtOAc-hexanes). Green crystalline solid. ¹H NMR (300 MHz, CD₂Cl₂): δ 16.47 (s, 1H), 8.59 (s, 1H), 7.43 (br, 8H), 6.91 (d, ³J_(HH)=5.1 Hz, 3H), 4.97 (m, 1H), 4.38 (s, 2H), 4.10 (s, 2H), 2.53 (s, 6H), 1.34 (br, 6H).

Catalyst 7b (i.e. compound 7 wherein R=ethyl). Obtained in a 68% yield after column chromatography on silica gel (eluted with 1:5 EtOAc-hexanes). Green crystalline solid ¹H NMR (300 MHz, CD₂Cl₂): δ 16.48 (s, 1H), 8.56 (br, 1H), 7.53 (m, 8H), 6.89 (d, ³J_(HH)=6.6 Hz, 3H), 4.95 (m, 1H), 4.42 (s, 2H), 4.10 (s, 2H), 2.93 (br, 4H), 1.37 (br, 12H).

Catalyst 7c (i.e. compound 7 wherein R=isopropyl). Obtained in a 77% yield as a green crystalline solid. ¹H NMR (300 MHz, C₆D₆): δ 16.65 (s), 16.46 (s), 9.18 (m), 7.90 (d), 7.40-6.93 (m), 6.59 (t), 6.34 (d, ³J_(HH)=7.5 Hz), 4.47 (m), 3.80-3.32 (m), 2.66 (br), 1.95-1.12 (m).

Example 3 Catalyst Performance in RCM

Ring-closing metathesis of dimethyl 2,2-di(2-methylallyl)malonate. Catalyst was added to a 0.1 M solution of dimethyl 2,2-di(2-methylallyl)malonate in CH₂Cl₂ in a round bottom (r.b.) flask. The flask was equipped with a reflux condenser and a bubbler outlet. The reaction mixture was sparged with argon for 5 min, then heated to desired temperature. Reaction progress was monitored by GC analysis of aliquots after removing the catalyst by treating the aliquot with 1M solution of THMP in IPA, heating the quenched mixture at 60° C. for 1 h, diluting it with water and extraction with EtOAc. The activity of catalysts of the invention were compared with the olefin metathesis catalyst (A) shown below:

TABLE 3 A

RCM of dimethyl 2,2-di(2-methylallyl) malonate with 5 mol % of A at 40° C. Time (min) Starting Material (GC %) Product (GC %) 30 91.9 3.0 60 92.4 4.2 180 84.3 15.7 1080 49.7 44.7 1440 42.4 49.8 2520 38.1 54.5

TABLE 4 RCM of dimethyl 2,2-di(2-methylallyl)malonate with 5 mol % of 6a at 40° C. Time (min) Starting Material (GC %) Product (GC %) 15 16.2 80.9 30 12.1 83.7 45 11.2 85.4 60 11.1 86.4 90 11.0 87.5 120 10.9 86.7 240 10.9 86.8

TABLE 5 RCM of dimethyl 2,2-di(2-methylallyl)malonate with 5 mol % of 6b at 40° C. Time (min) Starting Material (GC %) Product (GC %) 15 34.0 61.5 30 30.1 69.9 45 28.7 70.7 60 28.0 70.9 120 27.1 70.6 240 27.7 72.3 480 27.2 72.8

TABLE 6 RCM of dimethyl 2,2-di(2-methylallyl)malonate with 5 mol % of 6c at 40° C. Time (min) Starting Material (GC %) Product (GC %) 15 25.2 71.5 30 23.0 73.0 45 22.1 73.1 60 21.9 74.3 90 21.2 75.0 120 20.8 75.5 240 19.2 75.1

TABLE 7 RCM of dimethyl 2,2-di(2-methylallyl)malonate with 5 mol % of 6c at 30° C. Time (min) Starting Material (GC %) Product (GC %) 15 37.9 54.0 30 27.9 65.5 45 25.7 67.2 60 25.8 69.8 240 22.7 69.8 1140 20.7 69.5

TABLE 8 RCM of dimethyl 2,2-di(2-methylallyl)malonate with 1 mol % of 6c at 30° C. Time (min) Starting Material (GC %) Product (GC %) 15 50.9 46.3 30 47.6 49.4 45 46.6 51.0 60 45.5 51.6 90 44.2 52.8 120 44.0 53.7 360 41.2 54.9

TABLE 9 RCM of dimethyl 2,2-di(2-methylallyl)malonate with 5 mol % of 7a at 40° C. Time (h) Starting Material (GC %) Product (GC %) 0.5 65.8 30.6 1 52.3 44.7 3 31.5 65.1 18 28.4 69.9 24 28.3 70.0 42 27.5 68.8

TABLE 10 RCM of dimethyl 2,2-di(2-methylallyl)malonate with 5 mol % of 7b at 40° C. Time (h) Starting material (GC %) Product (GC %) 0.25 96.7 0.7 0.50 89.3 3.3 0.75 81.8 11.8 1 71.1 21.5 2 57.7 34.7 4 51.4 42.9 8 38.9 55.9 24 36.4 58.6

TABLE 11 RCM of dimethyl 2,2-di(2-methylallyl)malonate with 5 mol % of 7c at 40° C. Time (h) Starting Material (GC %) Product (GC %) 0.25 97.2 0.7 0.50 93.8 2.9 0.75 87.2 9.3 1 81.7 15.6 1.5 71.9 24.2 2 69.7 27.5 6 63.4 32.0 24 63.4 32.5

The results of the RCM performed with second generation catalysts and second generation catalysts with chelating carbene ligands reported above are further illustrated in the charts shown in FIG. 2 and FIG. 3. FIG. 2 shows that catalysts 6a, 6b and 6c perform much better than catalyst A in the RCM of compound 1. Indeed, the reactions catalyzed by 6a, 6b and 6c reach much higher conversions (between about 70% and about 90% conversion) compared to the reactions catalyzed by A (about 20% conversion). Additionally, the data represented on FIG. 2 demonstrate that catalysts 6a, 6b and 6c require short reaction times and mild temperatures to reach high conversions. For example, catalyst 6a gives a high conversion (i.e., greater than 80%) within only 15 minutes at 40° C., compared to 7 hours at 60° C. for catalyst 12. FIG. 3 shows that catalysts 7a, 7b and 7c are also more active than A in the RCM of compound 1, but are less active than catalysts 6a, 6b and 6c.

Example 4 Cross Metathesis Studies

Catalyst performance in cross-metatheses involving hindered olefins Inside the glovebox, a 4-mL vials was charged with approximately 1 mL of the appropriate hindered olefin solution (2M in CH₂Cl₂) followed by one equivalent of 5-hexene. The appropriate amount of the tested catalyst was added to the vial; after which it was sealed and heated to desired temperature. Reaction progress was monitored by GC analysis of aliquots after removing the catalyst by treating the aliquot with 1M solution of THMP in IPA, heating the quenched mixture at 60° C. for 1 h, diluting it with water and extraction with EtOAc. An identical cross-metathesis reaction was run with A for comparison.

Cross metathesis (CM) of 5-decene (5C₁₀) and 2,5-dimethyl-3-hexene using 1 mol % of 6a and A at 40° C.

TABLE 12

Results of CM of 5C₁₀ and 2,5-dimethyl-3-hexene using 1 mol % of 6a and A at 40° C. Product (GC %) 0.5 h 1 h 40 h 6a 20.0 23.9 29.9 A 11.8 15.3 7.8

Cross metathesis of 5-decene, 5C₁₀, and 2-methyl-1-nonene using 1 mol % of 6b, 6c, 6a and A at 40° C.

TABLE 13

Results of CM of 5C₁₀ and 2-methyl-1-nonene using 1 mol % of 6b, 6c, 6a and A at 40° C. Product (GC %) 1 h 3 h 6 h 6b 27.4 28.4 29.0 6c 22.2 23.5 24.0 6a 20.1 19.5 20.0 A 15.2 21.7 25.6

Example 5

Catalyst performance in self-metathesis of methyl oleate Inside the glovebox, a 4-mL vial was charged with approximately 10 g of methyl oleate. The appropriate amount of a stock solution of 6a in benzene was added to the vial, after which it was sealed and heated to 40° C. Reaction progress was monitored by GC analysis of aliquots after removing the catalyst by treating the aliquot with 1M solution of THMP in IPA, heating the quenched mixture at 60° C. for 1 h, diluting it with water and extraction with EtOAc.

Self metathesis (SM) of neat methyl oleate using 2, 5 and 20 ppm of 6a and A at 40° C.

TABLE 14

results of SM of neat methyl oleate using 2, 5 and 20 ppm of 6a and A at 40° C. Maximum conversion^(a) reached at, min 2 ppm 5 ppm 20 ppm 6a 30 10 5 A 30 10 <10 ^(a)Maximum conversion in this reaction corresponds to a mixture containing 50 mol % of the starting material and 25 mol % of each of the products (25 mol % 9-octadecene and 25 mol % 1,18-dimethyl-octadecenoate)

Example 6 Preparation of Salt 10

Preparation of Dianine 9. This is a two step procedure. In the first step, a 40% solution of glyoxal in water (465 μl, 4.1 mmol) was added to 3,5-di-tert-butylaniline (1.83 g, 8.9 mmol) in isopropanol (16 ml) and water (16 ml) at 0° C. The reaction stirred for 7 hours and during this time it warmed to room temperature. The reaction mixture was filtered through a glass frit; the filtrate was dissolved in CH₂Cl₂, dried over MgSO₄, filtered through another glass flit and concentrated. This crude reaction product was then dissolved in Et₂O (50 ml) and added to LAH (570 mg, 15 mmol) in Et₂O (50 ml) at 0° C. The reaction stirred for 36 hours and warmed to room temperature. The reaction was quenched with H₂O (570 μl), 15% NaOH/H₂O (570 μl), H₂O (2 ml), filtered through a glass frit dried over MgSO₄, filtered through another glass frit and concentrated. The reaction mixture was then purified by flash column chromatography (30% EtOAc/Hexanes) to yield 9 (786 mg, 36% over two steps) as an oil. ¹H NMR (300 MHz, CDCl₃) δ 6.85 (2H, t, J=1.5 Hz), 6.55 (4H, d, J=1.8 Hz), 5.31 (2H, s), 3.45 (4H, s), 1.31 (36H, s); ¹³C (75 MHz, CDCl₃) δ 152.1, 147.8, 112.8, 107.9, 44.1, 35.1, 31.7; HRMS (EI+) calc for C₃₀H₄₉N₂, 437.3896. Found 437.3902.

Preparation of NHC ligand precursor 10. To diamine 9 (786 mg, 1.8 mmol), was added (EtO)₃CH (3 ml, 18 mmol), NH₄BF₄ (189 mg, 1.8 mmol) and formic acid (2 drops). The reactions stirred at 90° C. for 48 hours. Et₂O was added to precipitate the salt. The reaction mixture was then filtered and the solids were washed with Et₂O and collected to yield 8 (633 mg, 66%) as a white solid. ¹H NMR (300 MHz, CDCl₃) δ 8.57 (1H, s), 7.42 (2H, t, J=1.5 Hz), 7.23 (4H, d, J=1.8 Hz), 4.69 (4H, s), 1.32 (36H, s); ¹³C (75 MHz, CDCl₃) δ 153.6, 151.4, 135.4, 123.1, 114.9, 50.5, 35.4, 31.5.

Alternate preparation of diamine 9:

N,N′-Bis(3,5-di-t-butylphenyl)oxamide. Oxalyl chloride (2.16 mL, 25 mmol) was added dropwise to a stirred solution of 3,5-di-t-butylaniline (10.28 g, 50 mmol) and triethylamine (7.0 mL, 50 mmol) in THF (200 mL) at 0° C. Upon addition, the reaction was allowed to warm up to r.t. and stirred for 1 h. The reaction mixture was then concentrated in vacuo and diluted with water (100 mL). The white precipitate was collected by filtration, washed with dilute HCl (100 mL), water (2×100 mL), and dried in vacuo. Obtained 9.07 g (78%) of N,N′-Bis(3,5-di-t-butylphenyl)oxamide as a white solid.

N,N′-Bis(3,5-di-t-butylphenyl)ethylenediamine (9). A 1M solution of BH₃-THF in THF (125 mL, 125 mmol) was added dropwise with stirring to the solid oxamide (9.06 g, 19.52 mmol) at r.t. The resulting homogeneous mixture was then refluxed for 15 h, allowed to cool down to r.t. and carefully quenched by adding water. The mixture was then concentrated and extracted with ether. Column chromatography (2:1 hexanes—dichloromethane, silica gel) afforded 6.51 g (76%) of pure 9 as a colorless oil and 1.27 g of impure 9 (contaminated with 3,5-di-t-butylaniline) which was subjected to a second chromatographic purification. The combined yield of 9 was 86%. ¹H NMR (300 MHz, CDCl₃) δ 6.85 (2H, t, J=1.5 Hz), 6.55 (4H, d, J=1.8 Hz), 5.31 (2H, s), 3.45 (4H, s), 1.31 (36H, s); ¹³C (75 MHz, CDCl₃) δ 152.1, 147.8, 112.8, 107.9, 44.1, 35.1, 31.7; HRMS (EI+) calc for C₃₀H₄₉N₂, 437.3896. Found 437.3902.

Example 7 Preparation of Catalyst 12

Preparation of Catalyst 12. NHC ligand precursor 10 (156 mg, 0.3 mmol), KOt-Bu(F₆) (66 mg, 0.3 mmol), and ruthenium complex 11 (132 mg, 0.22 mmol) were all combined in toluene in a glove box. The flask was removed and stirred at 60° C. for 18 hours in a fume hood. The reaction mixture was then directly purified by flash column chromatography (5% Et₂O/Hexanes, run 2 times) to yield catalyst 12 (34 mg, 20%) as a green oil. The catalyst was then lyophilized from benzene to give a pale green solid. It should be noted that by ¹H NMR the conversion to 12 is 50%. ¹H NMR (300 MHz, CDCl₃) δ 16.91 (1H, s), 8.14-8.13 (2H, m), 7.73 (2H, m), 7.64 (1H, m), 7.52 (1H, m), 7.06-6.92 (2H, m), 6.62 (1H, t, J=7.5 Hz), 6.31 (1H, d, J=8.4 Hz), 4.47 (1H, quint, J=6 Hz), 3.51 (4H, s), 1.51 (18H, s), 1.35 (6H, d, J=6 Hz), 1.24 (18H, s); HRMS (EI+) calc for C₄₁H₅₈N₂OCl₂Ru 766.2970. Found 766.3007. FIG. 4 depicts the single crystal X-ray structure was obtained for catalyst 12.

Example 8 Catalyst Activity Studies

Preparation of stock solutions. Catalyst 12 (14 mg) was placed in a 2 ml volumetric flask and taken into a glove box. In the glove box, 2 ml of CD₂Cl₂ was added to make stock solution Z. 0.44 ml of Z was then transferred to another 2 ml volumetric flask and diluted to 2 ml with CD₂Cl₂ to make stock solution Y.

Reaction Scheme 10.

In a glove box, 0.44 ml of stock solution Z (3.1 mg of 12, 0.004 mmol) was transferred to a screw cap NMR tube. CD₂Cl₂ (0.36 ml) was added and then 1 (21.5 μl, 0.08 mmol). The NMR tube was sealed, removed from the glove box and heated to 30° C. FIG. 5 is a graph of the conversion over time, demonstrating the dramatically improved reactivity 12 shows for ring-closing metathesis (RCM) to form tetrasubstituted olefins.

This study was repeated in C₆D₆ at 60° C. to examine the impact of temperature. Catalyst 12 (3.1 mg, 0.004 mmol) and C₆D₆ (0.8 ml) were combined in a screw cap NMR tube and 1 (21.5 μl, 0.08 mmol) was added. The NMR tube was sealed, removed from the glove box and heated to 60° C. A graph of conversion over time is shown in FIG. 6. As can be seen, after 24 hours 88% conversion has been achieved, and 83% conversion is achieved in only 7 hours.

Example 9 RCM Studies with Less Hindered Olefins

In a glove box, 0.4 ml of stock solution Y (0.6 mg of 12, 0.0008 mmol) was transferred to a screw cap NMR tube. CD₂Cl₂ (0.4 ml) was added and the NMR tube was sealed and transferred to a 500 MHz NMR which was warmed to 30° C. The NMR tube was then ejected, 13 (20.5 μl, 0.08 mmol) was added and the tube was injected for data collection. A graph of conversion over time is shown in FIG. 7.

In a glove box, 0.4 ml of stock solution Y (0.6 mg of 12, 0.0008 mmol) was transferred to a screw cap NMR tube. CD₂Cl₂ (0.4 ml) was added and the NMR tube was sealed and transferred to a 500 MHz NMR which was warmed to 30° C. The NMR tube was then ejected, 15 (19.5 μl, 0.08 mmol) was added and the tube was injected for data collection. FIG. 8 shows a graph of the conversion over time.

Example 10 Stability Studies

A striking feature of catalyst 12 is its stability. In solution (CH₂Cl₂ or Benzene), in the absence of substrate, it is stable for at least 4 weeks. As a solid, 12 is stable in air for at least 5 weeks. Finally, during the catalytic reactions described above, for the reactions performed at 30° C. the only time point the original catalyst was not observed by ¹H NMR was 162 hours. For the reaction performed at 60° C., none of the original catalyst was observed by ¹H NMR at 24.8 hours. Overall, catalyst 12 is highly stable.

Example 11 Preparation of Catalyst-18

Catalyst-18. NHC ligand precursor 10 (14 mg, 0.03 mmol), KOt-Bu(F₆) (6 mg, 0.03 mmol), and ruthenium complex 17 (14 mg, 0.02 mmol) were all combined in C₆D₆ in a screw cap NMR tube in a glove box. The NMR tube was removed and heated at 60° C. for 1 hour in a fume hood. Conversion to catalyst 18 was determined to be 52% by proton NMR. ¹H NMR (300 MHz, CDCl₃) δ 19.43 (1H, s).

It should be noted that complex 18 is relatively unstable. The phosphine analogue in which the pyridine ligand is replaced by PCy₃ is also unstable. It is believed that the tert-butyl groups on the NHC are so large that they actively dissosciate the pyridine and phosphine respectively. The transient stability makes these complexes less suitable for catalysis.

Example 12 Preparation of an NHC with Smaller Bis-Meta Substitution

Diamine salt 20. This is a two step procedure. In the first step, a 40% solution of glyoxal in water (1.15 ml, 10 mmol) was added to 3,5-di-methylaniline (2.5 ml, 20 mmol) in isopropanol (40 ml) and water (40 ml) at 0° C. The reaction stirred for 7 hours and during this time it warmed to room temperature. The reaction mixture was filtered through a glass frit; the filtrate was dissolved in CH₂Cl₂, dried over MgSO₄, filtered through another glass frit and concentrated. This crude reaction product was then dissolved in THF (37 ml) and to this at 0° C. was added NaBH₄ (1.5 g, 40 mmol). Concentrated HCl (1.6 ml) was added dropwise over 25 min. The reaction was stirred for 1 hour and then 4N HCl (75 ml) was added. The reaction was stirred for 1 hour and then filtered. The filtrate was wash extensively with Et₂O to give diamine salt 20 (438 mg, 13% over 2 steps) as an off white solid. ¹H NMR (300 MHz, CDCl₃) δ 6.84 (4H, s), 6.76 (2H, s), 3.62 (4H, s), 2.25 (12H, s).

NHC ligand precursor 21. HC(OEt)₃ (10 ml) was added to diamine salt 20 and the reaction was stirred at 90° C. for 14 hours. The reaction mixture was filtered and washed with Et₂O to give NHC ligand precursor 21 (290 mg, 71%) as an off white solid. ¹H NMR (300 MHz, DMSO(D₆) δ 9.89 (1H, s), 7.29 (4H, s), 7.02 (2H, s), 4.54 (4H, s), 2.51-2.49 (12H, m). HRMS (EI+) calc for C₁₉H₂₃N₂ 279.18613. Found 279.18572.

Catalyst 22. NHC ligand precursor 21 (9 mg, 0.03 mmol), KOt-Bu(F₆) (6 mg, 0.03 mmol), and ruthenium complex 911 (13 mg, 0.02 mmol) were all combined in C₆D₆ in a screw cap NMR tube in a glove box. The NMR tube was removed and heated at 60° C. for 2.5 hour in a fume hood. Conversion to catalyst 22 was determined to be 14% by proton NMR. ¹H NMR (300 MHz, CDCl₃) δ 17.19 (1H, s).

It should be noted that complex 22 is relatively unstable. It seems that the meta-methyl groups are not large enough and the complex is difficult to handle without decomposition. For this reason, this complex is unattractive for catalysis.

Example 13 Preparation of Unsaturated Meta-Substituted NHC Ligands

NHC ligand precursor 23. A solution of 3,5-ditertbutylaniline (3 g, 14.6 mmol) in toluene (5 ml) was added to a solution of paraformaldehyde (220 mg, 7.3 mmol) in toluene (5 ml). The reaction was then stirred at 100° C. for 1.5 hours. The reaction was cooled to 40° C. and 6N HCl (1.2 ml, 7.3 mmol) was added. The reaction was stirred for 5 minutes, glyoxal (837 μl, 7.3 mmol) was added and the reaction was stirred another 5 minutes. The reaction was stirred at 100° C. for 14 hours, cooled to RT and purified by column chromatography (5% MeOH/CH₂Cl₂) to yield a brown foam. This foam was washed with Et₂O to yield 806 mg (23%) of 23 as a white solid. ¹H NMR (300 MHz, CDCl₃) δ 11.89 (br, 1H), 7.78-7.76 (m, 6H), 7.59 (s, 2H), 1.42 (s, 36H); ¹³C (75 MHz, CDCl₃)δ; HRMS (EI+) calc for C₃₁H₄₅N₂, 445.3583. Found 445.3561.

Example 14 Preparation of Catalyst 24

Ruthenium Catalyst 24. In a glove box, NHC ligand precursor 23 (63 mg, 0.13 mmol), ruthenium precursor 11 (78 mg, 0.13 mmol) and KOt-Bu(F₆) (29 mg, 0.13 mmol) were combined in toluene. The flask was sealed, removed from the glove box and stirred at 60° C. for 18 hours. The reaction was concentrated and purified by flash column chromatography (5%->20% Et₂O/Pent). There were 3 bands that could be isolated from this column, first 2 brown bands and then one green band. The second brown band was the desired product; however, it was not completely pure after one column. Recolumning in 10% Et₂O/Pentane gave a brown oil product completely pure by ¹H NMR (9 mg, 9%) and another fraction still slightly impure (18 mg, 18%). The products were lyophilized from benzene to give solids. ¹H NMR (300 MHz, CDCl₃) δ 16.78 (s, 1H), 8.13 (br, 2H), 7.74-7.62 (m, 4H), 7.07-7.04 (m, 1H), 6.97 (dd, J=3, 1.5 Hz, 1H), 6.66 (t, J=7.5 Hz, 3H), 6.34 (d, J=8.4 Hz, 1H), 4.49 (sept, J=6 Hz, 1H), 1.44 (d, J=6 Hz, 6H), 1.44 (br, 18H), 1.18 (br, 18H); ¹³C (75 MHz, CDCl₃)₆; HRMS (EI+) calc for C₄₁H₅₆Cl₂N₂ORu, 764.2814. Found 764.2842.

Example 15 Preparation of Catalyst 25

Ruthenium Catalyst 25. In a glove box, NHC ligand precursor 23 (162 mg, 0.34 mmol), ruthenium precursor 5 (150 mg, 0.27 mmol) and KOt-Bu(F₆) (74 mg, 0.34 mmol) were combined in C₆D₆ and stirred at RT for 2.5 hours. The flask was sealed, removed from the glove box and the reaction was concentrated and purified by flash column chromatography (2.5%->5% Et₂O/Pent) to yield a brown oil. The brown oil was lyophilized from benzene to give 25 as a brown solid (66 mg, 25%). ¹H NMR (300 MHz, CDCl₃) δ 20.07 (d, J=10.5 Hz, 1H), 8.03 (br, 2H), 7.60 (t, 1.8 Hz, 1H), 6.86-6.81 (m, 2H), 6.51-6.47 (m, 1H), 1.81-1.07 (m).

Example 16 Preparation of Catalyst 26

Ruthenium Catalyst 26. In a screw cap NMR tube, ruthenium compound 25 (10 mg, 0.01 mmol), 2-isopropoxy-3-vinylbiphenyl (5 mg, 0.02 mmol) and CuCl (1 mg, 0.01 mmol) were combined in CD₂Cl₂ (1 ml) in the glove box. The reaction was heated at 40° C. for 29 hours, concentrated and purified by column chromatography (10%-->25% Et₂O/Pentange) to yield a grayish green oil. This oil was lyophilized from benzene to yield 26 as a solid (2 mg, 25%). ¹H NMR (300 MHz, CDCl₃) δ 16.77 (s, 1H), 7.89 (s, 1H), 7.66-7.59 (m, 6H), 7.50-7.38 (m, 7H), 7.02 (t, J=4.5 Hz, 1H), 6.72 (dd, J=3.6, 1.2 Hz, 1H), 4.45 (sept, J=3.6 Hz, 1H), 1.47 (s, 18H), 1.30 (s, 18H), 0.95 (d, J=3.6 Hz, 6H).

Example 17 Preparation of Para-Substituted NHC Ligand

Reaction Scheme 21

NHC ligand precursor 27. Glyoxal (1.92 ml, 16.8 mmol) was added to a solution of 4-tertbutylaniline (5.87 ml, 37 mmol), i-PrOH (60 ml) and water (60 ml). The reaction was stirred for 1 hour and then the liquids were decanted off. The remaining sticky solid was washed with i-PrOH and then any remaining solvent was removed under vacuum. THF (62 ml) was then added to the flask and it was cooled to 0° C. NaBH₄ (2.57 g, 68 mmol) was added to the solution. Concentrated HCl (2.7 ml) was added dropwise over 0.5 hours, and the reaction was stirred for 2 hours. 4N HCl (150 ml) was added slowly and the reaction was stirred for 0.5 hours, filtered and the filtrate was washed with Et₂O to give a white solid. To this filtrate was added HC(OEt)₃ (20 ml) and the reaction was stirred at 100° C. for 18 hours. The reaction was filtered. The filtrate was washed with Et₂O to give 27 as a white solid (80 mg, 1%). ¹H NMR (300 MHz, CDCl₃) δ 11.35 (br, 1H), 7.89 (br, 4H), 7.38 (br, 4H), 4.44 (br, 4H), 1.15 (s, 18H); ¹³C (75 MHz, CDCl₃) δ 151.1, 150.9, 133.0, 127.3, 118.6, 48.7, 34.8, 31.3; HRMS (EI+) calc for C₂₃H₃₁N₂ 335.2487. Found 335.2476.

Example 18 Preparation of Catalyst 28

Ruthenium Compound 928 (Comparative). In a glove box, NHC ligand precursor 27 (5 mg, 0.014 mmol), ruthenium precursor 17 (10 mg, 0.014 mmol) and KOt-Bu(F₆) (3 mg, 0.014 mmol) were combined in C₆D₆ in a screw cap NMR tube. The tube was removed from the box and immersed in a 60° C. oil bath. The solution immediately turned brown and a new species (28) was transiently observed. ¹H NMR (300 MHz, CDCl₃) δ 19.46 (d, J=6 Hz).

Example 19 Catalyst Activity

Standard activity tests were used to determined the utility of the new catalysts of the invention.

Catalyst 24.

Preparation of stock solutions. Catalyst 24 (9 mg) was placed in a 2 ml volumetric flask and taken into a glove box. In the glove box, 2 ml of CD₂Cl₂ was added to make stock solution X. 0.33 ml of X was then transferred to another 2 ml volumetric flask and diluted to 2 ml with CD₂Cl₂ to make stock solution W.

In a glove box, 0.67 ml of stock solution X (3 mg of 24, 0.004 mmol) was transferred to a screw cap NMR tube. CD₂Cl₂ (0.13 ml) was added and then 1 (21.5 μl, 0.08 mmol). The NMR tube was sealed, removed from the glove box and heated to 30° C. FIG. 9 shows the graph of conversion over time.

This experiment was repeated in C₆D₆ at 60° C. to examine the impact of temperature. Catalyst 24 (3 mg, 0.004 mmol) and C₆D₆ (0.8 ml) were combined in a screw cap NMR tube and 1 (21.5 μl, 0.08 mmol) was added. The NMR tube was sealed, removed from the glove box and heated to 60° C. FIG. 10 is a graph of conversion over time in C₆D₆.

Example 20 RCM Activity with Less Hindered Olefins

In a glove box, 0.8 ml of stock solution W (0.6 mg of 24, 0.0008 mmol) was transferred to a screw cap NMR tube. The NMR tube was sealed and transferred to a 500 MHz NMR which was warmed to 30° C. The NMR tube was then ejected, 13 (20.5 μl, 0.08 mmol) was added and the tube was injected for data collection. FIG. 11 is a graph of the conversion over time.

In a glove box, 0.8 ml of stock solution W (0.6 mg of 24, 0.0008 mmol) was transferred to a screw cap NMR tube. The NMR tube was sealed and transferred to a 500 MHz NMR which was warmed to 30° C. The NMR tube was then ejected, 15 (19.5 μl, 0.08 mmol) was added and the tube was injected for data collection. FIG. 12 is a graph of the conversion over time.

Example 21 Activity Studies

Catalyst 25.

Preparation of stock solutions. Catalyst 25 (11 mg) was placed in a 2 ml volumetric flask and taken into a glove box. In the glove box, 2 ml of CD₂Cl₂ was added to make stock solution V. 0.4 ml of V was then transferred to another 2 ml volumetric flask and diluted to 2 ml with CD₂Cl₂ to make stock solution U.

Reaction Scheme 25

In a glove box, 0.55 ml of stock solution V (3 mg of 25, 0.003 mmol) was transferred to a screw cap NMR tube. CD₂Cl₂ (0.25 ml) was added and then 1 (21.5 μl, 0.08 mmol). The NMR tube was sealed, removed from the glove box and heated to 30° C. A graph conversion over time is shown in FIG. 13. No further conversion is observed after 2 hours.

This experiment was repeated in C₆D₆ at 60° C. to examine the impact of temperature. Catalyst 25 (3 mg, 0.003 mmol) and C₆D₆ (0.8 ml) were combined in a screw cap NMR tube and 10 (21.5 μl, 0.08 mmol) was added. The NMR tube was sealed and transferred to a 500 MHz NMR which was warmed to 60° C. The NMR tube was then ejected, 1 (21.5 μl, 0.08 mmol) was added and the tube was injected for data collection. FIG. 14 is a graph of the conversion over time.

Example 22 Activity Studies with Less Hindered Olefins

In a glove box, 0.55 ml of stock solution U (0.6 mg of 25, 0.0008 mmol) was transferred to a screw cap NMR tube and 0.25 ml of CD₂Cl₂ was added. The NMR tube was sealed and transferred to a 500 MHz NMR which was warmed to 30° C. The NMR tube was then ejected, 13 (20.5 μl, 0.08 mmol) was added and the tube was injected for data collection. FIG. 15 is a graph of the conversion over time.

In a glove box, 0.55 ml of stock solution U (0.6 mg of 25, 0.0008 mmol) was transferred to a screw cap NMR tube and 0.25 ml of CD₂Cl₂ was added. The NMR tube was sealed and transferred to a 500 MHz NMR which was warmed to 30° C. The NMR tube was then ejected, 15 (19.5 μl, 0.08 mmol) was added and the tube was injected for data collection. FIG. 16 is a graph of the conversion over time.

Example 23 Activity Study

Catalyst 26.

In a glove box, catalyst 26 (2 mg, 0.002 mmol) was combined with CD₂Cl₂ (0.4 ml) in a screw cap NMR tube. The NMR tube was sealed and transferred to a 500 MHz NMR which was warmed to 30° C. The NMR tube was then ejected, 1 (11 μl, 0.04 mmol) was added and the tube was injected for data collection. FIG. 17 is a graph of the conversion over time that illustrates the dramtic decrease in reaction time necessary, relative to catalyst 12, for catalyst 26 to give 90% conversion of 1 to 2.

Example 24 Activity of Catalysts 6a, 6c, 27a and 27c in the Ring-Closing Metathesis of Dimethyl 2,2-di(2-methylallyl)malonate

The procedure used was the same as that described in Example 3 using catalysts 27a and 27c. The results for 6a, 6c, 27a and 27c are shown in FIG. 18. The results shown in FIG. 18 demonstrate that catalysts 6a and 6c perform better than 27a and 27c in the ring-closing metathesis of dimethyl 2,2-di(2-methylallyl)malonate. These results indicate that a catalyst based on an NHC ligand that has an unsubstituted bridge between the nitrogen atoms performs better than a catalyst that has phenyl substitutents on each carbons of that same bridge.

Example 25 Ring-Closing Metathesis of Dimethyl 2,2-di(2-methylallyl)malonate Using 5 mol % of Catalysts 6a and 7a in Toluene at 40° C. and 60° C.

A procedure analogous to that described in Example 3 was used, except that methylene chloride was replaced with toluene. The results are shown in FIG. 19.

Example 26

Catalyst 12 and catalyst B were compared under identical reaction conditions for the production of tetrasubstituted olefins by RCM. The reactions were performed with 0.08 mmol of substrate, 0.004 mmol of catalyst, 0.8 ml of C₆D₆ at 60° C. A comparison table follows.

TABLE 15 RCM to form tetrasubstituted olefins. NR = no reaction.

Conversions (isolated yields) with catalysts Substrate (E = CO₂Et)

  30   93 (86)

>95 >95 (99)

  50   51 (47)

  85 >95 (99)

>95 >95

  43¹   78² ¹75% consumption of H. ²10% 2,6-dichlorobenzoquinone added. Without 2,6-dichlorobenzoquinone: 60% conversion to product, 95% consumption of H.

Two of these substrates, D and G, were completely converted to product with both catalysts. Catalyst 12 gave improved conversion relative to catalyst B for every other substrate except E. Substrate H warrants further discussion. Use of catalyst B gave a mixture of three compounds, with 43% conversion to product, 32% conversion to a rearranged byproduct and 25% remaining starting material (H). Use of catalyst 12 resulted in complete consumption of H, but with only 60% conversion to product and 40% conversion to the byproduct. Interestingly, catalyst 10 gave 43% conversion to the product and no byproduct formation. Ruthenium hydride species formed from the decomposition of ruthenium olefin metathesis catalysts are known to catalyze the migration of olefins at 40° C. in CD₂Cl₂. Hong, S. H.; Day, M. W.; Grubbs, R. H. J. Am. Chem. Soc. 2004, 126, 7414. Repeating the reactions using B and 12 with 10% 2,6-dichloroquinone added to consume any hydride formed, (Hong, S. H.; Sanders, D. P.; Lee, C. W.; Grubbs, R. H. J. Am. Chem. Soc. 2005, 127, 17160) catalyst B gave very poor conversion, but catalyst 12 gave 78% conversion to product with no byproduct formation. Overall, catalyst 12 performed as well as or better than B for all of the substrates.

Example 26 Comparison of Catalysts A, 12 and 7a in Different Ring-Closing Metathesis Reactions to Form Tetrasubstituted Olefins

A procedure similar to that described in Example 8 was used to set up the ring-closing metathesis reactions and to follow their progress. The results are summarized in Table 16.

TABLE 16 RCM to form tetrasubstituted olefins (E = CO₂Et; Ts = tosyl). NR = no reaction.

Conversions (isolated yields) [%] with catalysts C848, 12, and 7a Substrate A 12 7a

  30   93 (86) >95

>95 >95 (99) >95

  50   51 (47)   62

  85 >95 (99) >95

>95 >95 >95

  43^(a)   78^(b)   88 ^(a)75% consumption of 17. ^(b)10% 2,6-dichlorobenzoquinone added. Without 2,6-dichlorobenzoquinone: 60% conversion to product, 95% consumption of 17.

Example 27 Cross Metathesis (CM) Results with Catalyst 7a

General procedure for CM reactions. A reflux condenser was attached to a flame-dried 10 mL 2-neck round bottom flask and the apparatus was flushed with argon. The flask was charged with solid catalyst and a stir bar. The second neck was closed with a septum, and dry, degassed C₆H₆ (2.5 mL) was added via syringe. The reagents were then added simultaneously via syringe. The solution was heated to 60° C. using an oil bath, and was stirred under argon for 18 h. The solution was then cooled to room temperature and concentrated. Conversions were measured by ¹H NMR of this crude reaction mixture, and yields determined by isolating the desired products by silica gel column chromatography.

Example 28 Preparation of bis(pyridine) Catalyst 28

In a nitrogen-filled glove box, pyridine (3.0 mL) was added to catalyst 6a (0.1 g, 0.126 mmol) and the solution was stirred until all of 6a had dissolved. The desired product was isolated by precipitation with pentane (0.070 g, 0.104 mmol, 83% yield). Green crystalline solid. ¹H NMR (300 MHz, C₆D₆): δ 19.30 (s), 9.51 (d), 8.53 (m), 7.92 (d), 7.25-7.05 (m), 7.00-6.77 (m), 6.64 (m), 6.51 (t), 6.22 (t), 3.08-3.64 (m), 2.49 (s), 2.31 (s).

Example 29 Ring-Closing Metathesis Reactions Using Catalysts 6a and 7a

The ring-closing reactions described in Example 22 were repeated using catalysts 6a and 7a with of substrates 13 and 15 to form the corresponding di- and tri-substituted olefins. The results are shown in FIGS. 20-23. FIG. 20 is a graph of the conversion of 15 over time for the RCM reaction for catalyst 6a. FIG. 21 is a graph of the conversion of 13 over time for the RCM reaction for catalyst 6a. FIG. 22 is a graph of the conversion of 15 over time for the RCM reaction for catalyst 7a. FIG. 23 is a graph of the conversion of 13 over time for the RCM reaction for catalyst 7a. 

1. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst of formula (I):

wherein: X¹ and X² are independently anionic ligands; n is 0, 1 or 2; R⁹ and R¹⁰ are each independently hydrogen or a substituted or unsubstituted substituent selected from the group consisting of C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, C₂-C₂₀ alkynyl, aryl, C₁-C₂₀ carboxylate, C₁-C₂₀ alkoxy, C₂-C₂₀ alkenyloxy, C₂-C₂₀ alkynyloxy, aryloxy, C₂-C₂₀ alkoxycarbonyl, C₁-C₂₀ alkylthio, C₁-C₂₀ alkylsulfonyl and C₁-C₂₀ alkylsulfinyl; or R⁹ and R¹⁰ may optionally be linked together to form a cyclic structure via one of the listed substituents; m is 1 or 2; when m is 1, L is a neutral 2-electron donor ligand and may optionally be linked to R¹⁰ forming a chelating carbene ligand when n is zero; when m is 2, L is a heteroarene ligand; and NHC is an N-heterocyclic carbene ligand selected from formulas (III)-(V):

wherein R¹, R², and R³ are either: a) each R¹ is independently a primary or secondary C₁-C₄ alkyl group; each R² is independently H, a substituted or unsubstituted C₁-C₁₀ alkyl group, substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, or substituted or unsubstituted anthracenyl; and each R³ is independently H, a substituted or unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, or substituted or unsubstituted anthracenyl, or a functional group selected from the group consisting of halo, hydroxyl, sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso, sulfo, sulfonato, boryl, borono, phosphono, phosphonato, phosphinato, phospho, phosphino, and silyloxy; or b) R¹ is H; each R² is independently H, a substituted or unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, or substituted or unsubstituted anthracenyl; and each R³ is independently H, a substituted or unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, or substituted or unsubstituted anthracenyl or a functional group selected from the group consisting of halo, hydroxyl, sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso, sulfo, sulfonato, boryl, borono, phosphono, phosphonato, phosphinato, phospho, phosphino, and silyloxy; with the provisos that both R² substituents on the same phenyl ring are not H; R⁴ and R⁶ are each independently H, a substituted or unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted aryl, or in formulas (III) and (V), together with the carbons carrying them, form a substituted or unsubstituted, fused 4-8 membered carbocylic ring or a substituted or unsubstituted, fused aromatic ring; R⁵ and R⁷ are independently H, a substituted or unsubstituted C₁-C₈ alkyl group; and R⁸ is a C₁-C₁₂ alkyl or a C₃-C₁₂ cycloalkyl.
 2. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claim 1, wherein the NHC ligand is selected from the group consisting of


3. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claims 1 or 2, wherein: X¹ and X² are halide, or a substituted or unsubstituted group selected from the group consisting of benzoate, C₁-C₅ carboxylate, C₁-C₅ alkyl, phenoxy, C₁-C₅ alkoxy, C₁-C₅ alkylthio, aryl, and C₁-C₅ alkyl sulfonate; n is 0 or 1; R⁹ is hydrogen, C₁-C₅ alkyl or aryl; R¹⁰ is a substituted or unsubstituted group selected from the group consisting of C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, and aryl; m is 1; and L is selected from the group consisting of phosphine, sulfonated phosphine, phosphite, phosphinite, phosphonite, arsine, stibine, ether, amine, amide, imine, sulfoxide, carboxyl, nitrosyl, pyridine, and thioether, or is linked to R¹⁰ forming a chelating carbene ligand when n is
 0. 4. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claim 3, wherein: X¹ and X² are each halide, CF₃CO₂, CH₃, CO₂, CFH₂CO₂, (CH₃)₃CO, (CF₃)₂ (CH₃)CO, (CF₃)(CH₃)₂CO, PhO, MeO, EtO, tosylate, mesylate, or trifluoromethanesulfonate; n is 0 or 1; R⁹ is hydrogen, C₁-C₅ alkyl or aryl; R¹⁰ is a substituted or unsubstituted group selected from the group consisting of C₁-C₂₀ alkyl, C₂-C₂₀ alkenyl, and aryl; m is 1; and L is a phosphine of the formula PR′R″R′″, where R′, R″, and R′″ are each independently aryl, C₁-C₁₀ alkyl, or C₃-C₆ cycloalkyl, or is linked to R¹⁰ forming a chelating carbene ligand when n is
 0. 5. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claim 4, wherein: X¹ and X² are each chloride; n is 0; R⁹ is hydrogen; R¹⁰ is phenyl, vinyl or —C═C(CH₃)₂; m is 1; and L is selected from the group consisting of P(cyclohexyl)₃, P(cyclopentyl)₃, P(isopropyl)₃, and P(phenyl)₃, or is linked to R¹⁰ forming a chelating carbene ligand.
 6. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claim 5, wherein the catalyst of formula (I) is selected from the group consisting of:


7. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claim 3, wherein the catalyst of formula (I) is selected from the group consisting of:


8. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claim 5, wherein L is selected from the group consisting of P(cyclohexyl)₃, P(cyclopentyl)₃, P(isopropyl)₃, and P(phenyl)₃.
 9. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claim 3, wherein L is selected from the group consisting of P(cyclohexyl)₃, P(cyclopentyl)₃, P(isopropyl)₃, and P(phenyl)₃.
 10. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst selected from the group consisting of:

wherein: X¹ and X² are independently anionic ligands; n is 0, 1 or 2; and NHC is an N-heterocyclic carbene ligand comprising a 5-membered heterocyclic ring having a carbenic carbon atom and at least one nitrogen atom contained within the 5-membered heterocyclic ring, wherein the nitrogen atom is directly attached to the carbenic carbon atom and is substituted by a phenyl ring, and wherein the phenyl ring has a hydrogen at either or both ortho positions and is substituted at at least one ortho or meta position.
 11. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claim 10, wherein the NHC ligand is selected from a ligand of formula of formulas (II)-(V):

wherein R¹, R², and R³ are either: a) each R¹ is independently a primary or secondary C₁-C₄ alkyl group; each R² is independently H, a substituted or unsubstituted C₁-C₁₀ alkyl group, substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, or substituted or unsubstituted anthracenyl; and each R³ is independently H, a substituted or unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, or substituted or unsubstituted anthracenyl, or a functional group selected from the group consisting of halo, hydroxyl, sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso, sulfo, sulfonato, boryl, borono, phosphono, phosphonato, phosphinato, phospho, phosphino, and silyloxy; or b) R¹ is H; each R² is independently H, a substituted or unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, or substituted or unsubstituted anthracenyl; and each R³ is independently H, a substituted or unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted phenyl, substituted or unsubstituted naphthyl, or substituted or unsubstituted anthracenyl or a functional group selected from the group consisting of halo, hydroxyl, sulfhydryl, cyano, cyanato, thiocyanato, amino, nitro, nitroso, sulfo, sulfonato, boryl, borono, phosphono, phosphonato, phosphinato, phospho, phosphino, and silyloxy; with the provisos that both R² substituents on the same phenyl ring are not H; R⁴ and R⁶ are each independently H, a substituted or unsubstituted C₁-C₈ alkyl group, substituted or unsubstituted aryl, or, in formulas (III) and (V), together with the carbons carrying them, form a substituted or unsubstituted, fused 4-8 membered carbocylic ring or a substituted or unsubstituted, fused aromatic ring; R⁵ and R⁷ are independently H, a substituted or unsubstituted C₁-C₈ alkyl group; and R⁸ is a C₁-C₁₂ alkyl or a C₃-C₁₂ cycloalkyl.
 12. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claim 11, wherein the NHC ligand is selected from the group consisting of

where R¹ is methyl, ethyl, propyl, or isopropyl;

where R¹ is methyl, ethyl, propyl, or isopropyl;

where R² is tert-butyl;

where R² is tert-butyl;

where R¹ is methyl, ethyl, propyl, or isopropyl; R⁶ and R⁷ are hydrogen or methyl; and R⁸ is methyl; where R¹ is methyl, ethyl, propyl, or isopropyl; and R⁸ is methyl.
 13. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claim 10, 11, or 12, wherein X¹ and X² are each halide, CF₃CO₂, CH₃,CO₂, CFH₂ CO₂, (CH₃)₃CO, (CF₃)₂ (CH₃)CO, (CF₃)(CH₃)₂CO, PhO, MeO, EtO, tosylate, mesylate, or trifluoromethanesulfonate.
 14. An N-heterocyclic carbene (NHC) ruthenium olefin metathesis catalyst according to claim 13, wherein X¹ and X² are each chloride. 